Inner tube and method of making the same



June 21, 1949- J. c. CARLIN EI'AL 2,473,784

I INNER TUBE AND METHOI OF MAKING THE SAME Filed Nov. 9, 1944 5 sheets-seet (//////////////////////fi. //////////////b7///// 1`//////////////////////////,

[Mentor-.- JAMES C.CARL!N ROBERT' R. LLOYD rry.

June 21, 1949. J. c. CARLlN E'l'AL INNER TUBE AND METHOD OF MAKING THE SAME 5 Sheets-Sheet 2 Filed Nov. 9, 1944 oo jo' ,Kruje/dor JAMES C, CHRLIH June 21, 1949. J. c. CARLIN ETAL 2473784 INNER TUBE AND METHOD OF MAKING THE SAME Filed Nov. 9, 1944 3 Sheets-Sheet 3 Irwe'rdvrs:

.JAMES C. CARLIN ROBERT R'. LLOYD %fitoj Patented June 21, 1949 INN'ER TUBE AND METBOD OF MAKING THE SAME James C. Carli and Robert R.. Lloyd, No-rlstown, Pa., assigno-s to Lee Rubber & Tire Corporation, Conshohocke, Pa., a. corporation of New York Application November 9, 1944, Serial No. 562.730

1 Claim. 1

This invention relates generally to hollow articles made of synthetic rubber and more particularly to an improved Construction of synthetic rubber inner tube for pneumatic tires and to the method of splicng such tubes and other such annular inflatable articles of manufacture.

Heretofore and prior to the present invention, in the manufacture of such synthetic rubber articles as inner tubes employed as air containers within pneumatic tires, considerable difilculty has been encountered in obtaining a satisfactcry splice between the ends of the tubular stock of which the tube is formed.

Two methods of splicing are generally employed in the manufacture of pneumatic inner tubes. According to one method, the ends of the tubular stock of which the tube is formed are complementally skived to feather edges, after which the skived portions are bufied and coated with a suitable adhesive and then brought into overlapping relation to form a joint, this method resultin in what is conventionally known as a lapped splice. According to the other method, the opposite ends of the tubular stock are cut by means of a suitable cutting device, usually a hot knife, and the .freshly severed ends are then closely pressed together into abutting relation, the abutting ends being so held together until adhesion takes place between the freshly severed ends to produce what is now conventionally known as a :butt splice. In both cases, after the tube ends have been preliminarily joined together, the tube is placed in a curing mold wherein it is vulcanized to produce a permanent, integral union between the spliced parts.

At the present time, pneumatic inner tubes and l ke articles are being made practically exclusively of synthetic rubber, of which two types are gcnerally employed, one being of a composition now generally known and designated by the term GB-S" and the other of a composition generally known and designated by the term GR-I." These terms "GB-S" and "GR-I" are Government-designated terms for respectively identitying synthetic rubber of butadiene-styrene copolymer composition and synthetic rubber of isopreneisobutylene copolymer composition. mount difllculty with -both the GR-S and GR-I synthetic rubber compositions is that they lack adhesiveness of the order necessary to securely hold the spliced ends together while in the curing mold so as to obtain a satisfactory butt weld, while in the case of the GR-I composition, it is so impervious to gasses that upon-the generation of any gas between the spliced surfaces of the tube,

The paraas frequently occurs during the curing process to which the tube is subjected, objectionable blisters 'form within the splice because of the inability of the gas to escape from between the spliced portions of the tube. Moreover, the-gas so confined between the spliced suriaces of the tube interreres with proper, adhesion of the surfaces to be joined together with the result that dei'ectvc splices frequently occur. This blistering effect is especially pronounced in the case of GR-I tubes formed with lapped splices.

Also, because both the GR-I and the GR-S synthetic rubber compositions. are slow curing as compared with natural rubber, the extra thickness of the overlap in the case of a lapped splice necessitates such a prolonged curing time as to render lapped splices in tubes made of such synthetic rubber compositions economically unsatisfactory.

We have found that ,all of the aforementioned difliculties may be obviated by employing in conjunction with the butt splice method of forming pneumatic tubes a binding tape or band which 'is specially treated to render it capable of only temporary adherence to the particular synthetic rubber of which the tube is'formed and which is adapted, when wrapped about the splice, to firmly and securely hold together the abutting edges thereof in adhering contact when the tube is inflated preparatory to and during the curing process, the .tape or band being subsequently stripped from the tube upon its removal from the curing mold. i

Accordingly, it is among the principal objects ofthe present invention to provide a method of butt splicing tubes formed of synthetic rubber wherein a binding tape or band is employed which is of such character that it functions to hold the abutting edges of the tube together so efiectively during the curing operation that upon completion of the cure, the said edges will have been integrally and permanently secured together throughout their entiretcircunferential extent, the tape being so incompatible with the particular synthetic rubber composition of which the tube is formed as to permit of its being readily stripped from the tube upon removal thereof from the curing mold.

A further object of the present invention is to provide a pneumatic tube' formed of synthetic rubber having a butt-splice which is comparable in all material respects with the butt-splice of a tube formed of natural rubber, as well as to provide the means for and'method oi' producing such butt-splice without appreciably increasing the Other objects and advantages of the present invention will appear more iully hereinater, it being understood that the said invention consists substantially in the combination, arrangement, location and relative arrangement of the parts, as well as in the procedure by which the same are employed, as will be described herein, as shown in the drawings and as finally pointed out in the appendedclaim.

In the said accompanyins drawings:

Figure 1 is an elevational view. partially in section, of a portion o! an expanded tube with its severed ends shown in separated relation;

Figure 2 is a perspective view oi a portion of the tube shown flattened and with its severed ends in abutting relation;

Figure 3 is a perspective view of the flattened tube showing the binding tape or band wrapped about the abuttins edges of the tube;

Figure 4 is a sectiona view taken on the line 4-4 of Figura 3; i

Figure 5 is a view of the binding tape or band which is employed in accordance with the present invention;

Figure 6 is a view similar to Figure 1 but showing the severed ends ot the tube in abutting relation and wrapped with the binding tape preparatory to vulcanization of the tube splice in the curing mold;

Figure 7 is an elevational view oi the vulcahized tube with the binding tape stripped therefrom. the vulcanized splice being shown partially in section;

Figure 8 is a perspective view showing a modifled application oi' the bindin; tape to the tube;

Figure 9 is an elevational view showing a portion of the tube, treated as shown in Figura 8, innated preparatory to the curing operation; and

Figure 10 is a transverse section of the inflated tube taken on the line lI--ll of Figure 9.

Referring now more particularly to the drawings, it will 'be observed that the tube li, which is formed of either GR-S or GR-I synthetic rubber, is initialiy prepared in accordance with conventional practice followed in the making of buttsplice jcints by severing the tube stock to provide a. pair oi square cut edges ll and I! which are adapted to be brought into abutting relation as best shown in Figur-es 2, 3 and 4. 'As has been previously pointed out, due to the fact that both the GR-S and GR-I synthetic rubber compositions lack in themselves the adhesiveness necessary to securely hold the i'reshiy severed edges l l and !2 together, it is dimcult, i! not Impossible, to maintain said edges in contacting relation throughout their circumierential extents while the tube is innated preparatory to and during curing of the tube, particularly in view o! the fact that such process requires the tube to be inflated to a pressure which, while of low order,

nevertheless tends to and frequently does pull the abutting edges of the tube apart before the same are eflectively and integrally united by the vulcanizing process.

In order to overcome this dimculty, we employ a fabric tape or band ll which is adapted to be wrapped about the tube splice in the manner best shown in Figures 3 and 4 to hold the ireshly severed ends II and I! thereof in abutting contact with each other. Thistape or band Il is specially prepared in the form oi a bias cut narro w strip o! iabric, one surface o! which is eoated, as at ll, with an adhesive which is suitable for use with the particular synthetic rubber composition of which the tube may be for-med.

Thus, in the case of the tape or band designed for use with a tube iormed or GR-S synthetic rubber, the friction coating ll thereof is of GR-I synthetic rubber because the latter is not compatible with GR-S rubber and the tape therefore does not become integrally bonded to the tube when the latter is cured in the vulcanizing mold. In applying this tape so :[riction coated with GR-I rubber, the surface of the GR-S tube inthe immediate region of the splice is initially coated with an application oi natural rubber cement which has a vulcanizing aflinity for the GR-S rubber of the tube, but not !or the GR-I iriction coating of the tape. The rubber cement, however, provides a tacky surface to which the GR-I iri'ction coating of the tape ll adheres sufflciently to maintain it in place when wrapped about the splice, the tape thus serving to hold the severed ends of the tube stock together preliminarily to and during the vulcanization of the tube. Upon removal of the tube from the curing mold following vulcanization of the splice, the tape is stripped from the tube, the resultant tube splice being then of the form shown in Figure 7 with the severed ends of the tube integrally united, as at IS. The tape 14, of course, is readiiy stripped from the tube/ by reason of the fact that the friction coating thereot has no vulcanizing afflnity :for the tube stock or for the natural rubber cement which was applied to the surface oi the tube for adhesively' securing the tape in place.-

Inasmuch as this rubber cement does itselt have a vulcanizing aflinity for the GR-S rubber oi the tube, it becomes bonded to the latter as an integral part thereof during the curing process.

In the case of a tube formed of GR-I synthetic rubber, a binding tape or band I! is employed having a friction coating M of crude or natural rubber. In order to adhesively secure such tape to the tube when it is wrapped about the splice as shown in Figures 3 and 4, the surface of the tube throughout the region of the splice is rendered suitably tacky by the application thereto of a GR-I synthetic rubber cement or of a suitable solvent therefor, such as gasolene. The spliced tube, with the binding tape applied thereto as described, is then placed in the curing mold for vulcanization of the splice. Upon removal of the vulcanized tube from the mold, the tape is readily stripped therefrom'by reason of the fact that its Iriction coating or crude or natural rubber, having no vulcanzing aflinity i'or the GR-I rubber of the tube, is not permanently bonded or united thereto.

It will be observed that the binding tape or hand 13 is i'ormed of a woven fabric which is bias cut to provide it with a capacity for lengthwise Stretch to thereby enable it to extend with the tube as the latter is iniiated preparatory to placing it in the curing mold. As the tape is 'circumferentialiy extended upon inflation ot the tube about which it is wrapped, the tape is correspondingly contracted in its width in consequence of which it tends to draw or force the edges of the splice into such close contacting engazement as to insure -the formation of a splice which is uniformly good throughout its circumferential extent. Actually, this tendency of the binding tape to contract widthwise upon its being longitudinaly stretched so compresses the tube stock within the region thereo! which is embraced by the tape that upon subsequent cui-ing or the tube, its

wall thickness, in the immediate'region o! the splice and to either side of the central line thereof, is materially increased, as is indicated by the reference numeral IS in Figure 7. Due-to the fact that the external surface oi the tube is pressed into engagement with and so coni'orms to the contour of the internal walls of the curing mold, the extra thlckness IS formed in the region of the splice is disposed internally of the tube in the form of a relatively broad annular rib within which is included the tube splice. Thus. although from all outward appearances the tube splice of the present invention would appear to be oi conventional construction, it is actually oi' substantially greater body and therei'ore stronger than the conventional splice.

It will be apparent from the ioregoing that in the practice of the present invention no special equipment or apparatus other than ordinarily employed in the manufacture of butt-spliced tubes is required. The departure from conventional practice is in the application of the binding tape which is wrapped about the splice of the tube prior to its inflation and insertion in the curing mold, the tape being removabiy cemented in place as hereinbefore described; Preferably, the opposite ends of the applied tape zerave;

are overlapped (see Figura 3) to insure that' the splice is adequately covered throughout its entire extent.

In certain constructions of the inner tube. especially in the' larger sizes thereof, it is desirable to limit the application of the frictioncoated tape ll to that portion of the splice which extends circumferentialiy about the crown of the` In such cases, the tape extends' somewhat more than halt way around the tube' inflated tube.

splice, the remaining portion oi the splice being covered by a strip i'l of rubber having a vulcanizing aiiinity for the particular rubber composition of which the tube is principally formed.

As most clearly appears in Figures 8, 9 and 10, the auxiliary strip l'l ot rubber. which becomes permanently bonded or united to the tube upon vulcanization thereof, is disposed about the inner half of the circumierential splice. while the iriction-coated tape II, which may be stripped !rom the tube following 'curing thereof, is disposed about the outer halt oi the splice. The opposite ends of the tape I: overlap the proximate ends of the auxiliary rubber strip I'l, as at i', to insure that the splice is completely covered throughout its circumi'erential extent.

Of course, in applying the friction-coated tape I: about the tube as illustrated in Figures 8, 9 and 10, exactly the same procedure is fol-. lowed as described in the case where the tube splice is completely wrapped with the iriction tape, the adhesive coating of the latter being or such composition as has no vulcanizing' aiilnity for the particular rubber of which the tube is formed. However. inso far as concerns the auxiliary rubber strip ll, it is oi a composition which has an aflinity tor the tube stock, because such strip is intended to become integrally bonded to the tube about the inner half of the tube splice. Thus, in the case of a tube formed of GR-I synthetic rubber, the rubber strip I'I is also formed of GR-I rubber, while in the 'case of a tube formed ot GR-S synthetic rubber, the strip I'I is formed o! either natural rubber. or GR-s synthetic rubber, both oi' which have a vulcanizing ailinity for the GR-S synthetic rubber.

What is claimed as new and useful is:

In a method of splicing a pneumatic rubber tube which consists in complexnentally severing the opnoslte ends thereoi whfle in an uncured state to provide the same with treshly exposed surface& in joining together the severed ends oi' the tube with the exposed suriaces thereot in contacting relation. in applying about a substantial extent o! the tube joint a circumierentially extending !ab-ic tape having its inner surface treated with a material which is nonvulcanizably adherent to the rubber stock oi the tube. said tape being bias cut to provide it with a capacity for lengthwise Stretch, in inflatinz the tube preliminarily to curing ot the same in a curing mold, and in then cui-ing the inflated tube, said tape being so contracted in width upon the inflation oLthe tube and the corresponding lengthwise Stretch oi' the tape as to draw the tape-covered portion; oi' the tube stock together with a resulting increase in thickness oi said portion& v

JAMES C. CARLm. ROBERT R. LLOYD.

ammons cmu The following references are oi record in the me of this patent: i

UNITED STATES PATENTS Number v Name Date Re.12,6'71 Ma'ks July 9, 1907 &8,058 Woodward Oct. 23, 1894 Roberts July 22,1919 1,310A38 Roberts July 22, 1919 1,459,401 1511575 1,638,659

Goldthread Dec. 28, 1926. Fair-child Aug. 9, 1927 Davis Nov. 11, 1947 FUREIGN PATENTS Country Date Hottel June 19, 1923 

